Method of controlling power converter and power converter

ABSTRACT

A method of controlling a power converter is provided. The power converter generates a three-phase output power by switching an input power through a plurality of switches. The method includes steps of: acquiring a three-phase output command corresponding to the three-phase output power; comparing the three-phase output command with a control carrier to acquire a voltage phase angle corresponding to the three-phase output command; acquiring a three-phase current value of the three-phase output power; detecting the voltage phase angle and a positive/negative change of the three-phase current value to decide a zero-sequence voltage; composing the zero-sequence voltage and the three-phase output command to acquire a three-phase output expected value; comparing the three-phase expected values with the control carrier to acquire a turned-on time of each switch; and switching the input power to adjust the three-phase output power according to the turned-on time of each switch.

BACKGROUND Technical Field

The present disclosure relates to a method of controlling powerconverter and a power converter, and more particularly to a method ofcontrolling power converter and a power converter that are based on anAZSVPWM by using proper intervals to introduce zero-sequence voltage toreduce DC current ripple.

Description of Related Art

The statements in this section merely provide background informationrelated to the present disclosure and do not necessarily constituteprior art.

In various industrial applications, a power converter 100 shown in FIG.1 is often used to convert electrical energy. The power converter 100disposed between on the AC side and the DC side is used to convert theelectrical energy of the battery 200 and provides the required power tothe load 300. In particular, the place where the power converter 100 isconnected to the battery 200 may be referred to as the “DC side”, whichmay be batteries, solar panels, capacitors, etc. in different practicalapplications. The load side in FIG. 1 may also be referred to as the “ACside”, which can be motors, power grids, industrial products, etc. indifferent practical applications.

Please refer to FIG. 2 , which shows a circuit diagram of theconventional power converter. The power converter 100 is composed of athree-arm structure including six switches (each arm includes an upperarm switch S_(u1), S_(v1), S_(w1) and a lower arm switch S_(u2), S_(v2),S_(w2)). The output of each phase is connected to a center point of theupper arm switch and the corresponding lower arm switch, which is aknown circuit structure widely used in industrial products.

Please refer to FIG. 3 , which shows a block diagram of the systemstructure of pulse width modulation traditionally applied to the powerconverter. In different practical applications, the controller 400corresponding to the power converter 100 is designed in differentmanners. For example, when the load 300 is a voltage source, the powerconverter 100 is often used as an active front end, and therefore thecontroller 400 should adjust the power factor of the AC side. If theload 300 is a motor, the power converter 100 should be designed tocontrol various types of motors. Therefore, with different applications,the design of the controller 400 corresponding to the power converter100 is also different, but the purpose is to control the voltage on theAC side to achieve the purpose of control. Therefore, the controller 400generates a corresponding voltage command Vref to control the outputvoltage of the AC side. Moreover, the pulse width modulation (PWM)technology 500 can convert (modulate) the voltage command Vref to outputa switching signal to a switching element module of the power converter100 to output the corresponding voltage. As shown in FIG. 3 , the outputvoltage of the power converter 100 is a pulse voltage. Ideally, if thereis no loss in the system, the average value of the pulse voltage will bethe voltage command Vref.

Most of the pulse width modulation technology used in traditionalthree-phase power converters is a switching method called space vectorpulse width modulation (SVPWM), which is to compare the voltage commandof each of the three phases with a carrier ePWM. As shown in FIG. 4 ,when the phase voltage command Vref is greater than the carrier ePWM,the upper-arm switch is turned on, and the lower-arm switch is turnedoff. As shown in FIG. 5 , if the three-phase voltage commands v_(u)*,v_(v)*, v_(w)* are compared with the carrier ePWM, the switches of thethree-phase arms can be sorted out as shown in FIG. 5 (whenv_(u)*>v_(v)*>v_(w)*). By analyzing various combinations of voltagecommands and transfer output voltages to the d-q synchronization axis,which can be sorted into a space vector diagram composed of voltagevectors v₀-v₇, as shown in FIG. 6 . For example, v₁(100) represents theU-phase upper arm switch is turned on, the V-phase and W-phase lower armswitches are turned on, and the output voltages generated by v₀(000) andv₇(111) are all zero, so it is called the zero vector, and the remainingv₁-v₆ vectors are called active vectors. This PWM method has been widelyused in various power converter products.

FIG. 6 can explain the basic concept of SVPWM: the three-phase voltagecommands v_(u)*, v_(v)*, v_(w)* are transferred to the synchronizationaxis and then the angle θ between the voltage command v* and the q axisis acquired. The different angles θ make the voltage command v* fallwithin any vector triangle in FIG. 6 . This voltage command will besynthesized by the voltage vectors forming the triangle within oneswitching cycle. The voltage command v* falls in the triangular intervalcomposed of v₁, v₂, v₀, v₇. In this condition, in a PWM switching cycle,as shown in FIG. 5 , the output voltage vector is v₇-v₂-v₁-v₀-v₁-v₂-v₇in sequence, and Table 1 defines the relationship between the voltageintervals and the angle θ of voltage command v*.

TABLE 1 voltage intervals (R_(vol)) angle (θ) of voltage command v* I 0°-60° II  60°-120° III 120°-180° IV 180°-240° V 240°-300° VI 300°-360°

Different from the aforementioned SVPWM, there is another PWM switchingmethod called AZSVPWM, the principle of which is to replace the zerovectors (v₀, v₇) in a switching cycle with the active vectors (v₁-v₆),as shown in FIG. 7 (when v_(u)*>v_(v)*>v_(w)*). Unlike SVPWM, theswitching method of AZSVPWM is to compare the maximum (v_(u)*) andminimum (v_(w)*) of the three-phase voltage command with a carrier ePWM,and the intermediate value (v_(v)*) with a reverse carrier ePWM′.Compared with FIG. 5 , it can be found that the zero vector in SVPWM isreplaced by the active vector (v₃, v₆), that is, the zero vector v₇ isreplaced by the active vector v₆, and the zero vector v₀ is replaced bythe active vector v₃. Therefore, corresponding to the vector diagram ofFIG. 6 , the voltage command v* is composed of the vector falling on thehalf plane. This switching method can effectively reduce the common-modevoltage on the output side, and is often used in motor driverapplications, and this method has been widely discussed in academics andthe industry. On this basis, the technology proposed in the presentdisclosure is more commonly used in motor driver applications. It is atechnology based on AZSVPWM that uses an appropriate interval tointroduce zero-sequence voltage to reduce DC current ripple.

SUMMARY

An object of the present disclosure is to provide a method ofcontrolling a power converter to solve the problems of the existingtechnology.

In order to achieve the above-mentioned object, the power converterconverts an input power to generate a three-phase output power through aplurality of switches. The method includes steps of: acquiring athree-phase output commands corresponding to the three-phase outputpower; comparing the three-phase output command with a control carrierto acquire a voltage phase angle corresponding to the three-phase outputcommand according to the comparison result; acquiring a three-phasecurrent value of the three-phase output power; detecting the voltagephase angle and a positive/negative change of the three-phase currentvalue to decide that a zero-sequence voltage is a positive voltage, azero voltage, or a negative voltage; composing the zero-sequence voltageand the three-phase output command to acquire a three-phase outputexpected value; comparing the three-phase expected value with thecontrol carrier to acquire a turned-on time of each switch; switchingthe input power to adjust the three-phase output power according to theturned-on time of each switch.

In one embodiment, the method further includes steps of: building atable by a controller; determining the voltage phase angle and thepositive/negative change of the three-phase current value to query thetable to decide that the zero-sequence voltage is the positive voltage,the zero voltage, or the negative voltage. The table includes aplurality of voltage intervals and a plurality of current intervals, andeach voltage interval is corresponding to the plurality of currentintervals. Each voltage interval of the table correspondingly records aplurality of phase intervals. Each current interval of the table recordsthe positive/negative change of the three-phase current value. The tablerecords the zero-sequence voltage corresponding to each current intervalin the different voltage intervals is the positive voltage, the zerovoltage, or the negative voltage.

In one embodiment, the method further includes steps of: determiningthat the voltage phase angle falls into one of the plurality of phaseintervals; selecting correspondingly the voltage interval correspondingto one of the plurality of phase intervals in the table; receiving anddetermining the positive/negative change of the three-phase currentvalue, and selecting the corresponding current interval in the table;querying the table to decide that the zero-sequence voltage is thepositive voltage, the zero voltage, or the negative voltage according tothe selected voltage interval and the selected current interval.

In one embodiment, the plurality of phase intervals includes a firstphase interval [0, π/3], a second phase interval [π/3, 2π/3], a thirdphase interval [2π/3, π], a fourth phase interval [π, 4π/3], a fifthphase interval [4π/3, 5π/3], and a sixth phase interval [5π/3, 2π].

In one embodiment, the method further includes steps of: recording thethree-phase current value as a first current interval of the pluralityof current intervals when a U-phase current of the three-phase currentvalue is positive, a V-phase current is negative, and a W-phase currentis negative; recording the three-phase current value as a second currentinterval of the plurality of current intervals when the U-phase currentof the three-phase current value is positive, the V-phase current ispositive, and the W-phase current is negative; recording the three-phasecurrent value as a third current interval of the plurality of currentintervals when the U-phase current of the three-phase current value isnegative, the V-phase current is positive, and the W-phase current isnegative; recording the three-phase current value as a fourth currentinterval of the plurality of current intervals when the U-phase currentof the three-phase current value is negative, the V-phase current ispositive, and the W-phase current is positive; recording the three-phasecurrent value as a fifth current interval of the plurality of currentintervals when the U-phase current of the three-phase current value isnegative, the V-phase current is negative, and the W-phase current ispositive; recording the three-phase current value as a sixth currentinterval of the plurality of current intervals when the U-phase currentof the three-phase current value is positive, the V-phase current isnegative, and the W-phase current is positive.

In one embodiment, when the zero-sequence voltage is decided to be thepositive voltage, the method further includes steps of: acquiring a peakvalue of the control carrier in a switching cycle; acquiring a maximumvoltage command of the three-phase output command; calculating a firstvoltage difference between the peak value and the maximum voltagecommand as a magnitude of the positive voltage of the zero-sequencevoltage.

In one embodiment, when the zero-sequence voltage is decided to be thenegative voltage, the method further includes steps of: acquiring avalley value of the control carrier in a switching cycle; acquiring aminimum voltage command of the three-phase output command; calculating asecond voltage difference between the valley value and the minimumvoltage command as a magnitude of the negative voltage of thezero-sequence voltage.

In one embodiment, the control carrier incudes a first triangle wave anda second triangle wave, and a phase difference between the firsttriangle wave and the second triangle wave is π.

In one embodiment, the method further includes a step of: executing anAZSVPWM control to acquire the voltage phase angle corresponding to thethree-phase output command located on a two-phase coordinate axisaccording to the three-phase output command, the first triangle wave,and the second triangle wave.

In one embodiment, the power converter includes a DC-side capacitor, andthe DC-side capacitor is coupled to each of the switches, and the methodfurther includes a step of: acquiring the turned-on time of each switchby comparing the three-phase output expected value with the controlcarrier to reduce a current ripple of the DC-side capacitor.

Accordingly, the method of controlling the power converter proposed bythe present disclosure is based on the AZSVPWM, and the appropriatezero-sequence voltage is introduced to reduce DC current ripple.

Another object of the present disclosure is to provide a power converterto solve the problems of the existing technology.

In order to achieve the above-mentioned object, the power converterincludes a plurality of switches and a controller. The plurality ofswitches converts an input power to generate a three-phase output power.The controller includes a control carrier, wherein the controlleracquires a three-phase output command corresponding to the three-phaseoutput power, and acquires a voltage phase angle corresponding to thethree-phase output command. The controller detects a positive/negativechange of a three-phase current value of the three-phase output power.The controller builds a table, and the table incudes a plurality ofvoltage intervals and a plurality of current intervals, and each voltageinterval is corresponding to the plurality of current intervals. Eachvoltage interval of the table correspondingly records a plurality ofphase intervals. Each current interval of the table records thepositive/negative change of the three-phase current value. The tablerecords the zero-sequence voltage corresponding to each current intervalin the different voltage intervals is the positive voltage, the zerovoltage, or the negative voltage. The controller queries the table todetermine the voltage interval in which the voltage phase angle fallsaccording to the voltage phase angle and the three-phase current value,and decides that the zero-sequence voltage is the positive voltage, thezero voltage, or the negative voltage according to the current intervalcorresponding to the positive/negative change of the three-phase currentvalue. The controller composes the zero-sequence voltage and thethree-phase output command to acquire a three-phase output expectedvalue, and compares the three-phase expected value with the controlcarrier to acquire a turned-on time of each switch.

Accordingly, the power converter proposed by the present disclosure isbased on the AZSVPWM, and the appropriate zero-sequence voltage isintroduced to reduce DC current ripple.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary, and are intended toprovide further explanation of the present disclosure as claimed. Otheradvantages and features of the present disclosure will be apparent fromthe following description, drawings, and claims.

BRIEF DESCRIPTION OF DRAWINGS

The present disclosure can be more fully understood by reading thefollowing detailed description of the embodiment, with reference made tothe accompanying drawing as follows:

FIG. 1 is a schematic block diagram of a conventional power converter inapplication.

FIG. 2 is a circuit diagram of the conventional power converter.

FIG. 3 is a block diagram of the system structure of pulse widthmodulation traditionally applied to the power converter.

FIG. 4 is a schematic waveform of switching the conventional powerconverter in a PWM manner.

FIG. 5 is a schematic waveform of switching the conventional powerconverter in an SVPWM manner.

FIG. 6 is a space vector diagram composed of voltage vectors under theconventional SVPWM switching manner.

FIG. 7 is a schematic waveform of switching the power converter in anAZSVPWM manner.

FIG. 8A is a schematic waveform of the relationship between switchswitching and a DC current in a switching cycle under traditional SVPWMswitching.

FIG. 8B is a schematic waveform of the relationship between switchswitching and a DC current in a switching cycle under AZSVPWM switchingaccording to the present disclosure.

FIG. 9 is a space vector diagram composed of voltage vectors underAZSVPWM switching according to the present disclosure.

FIG. 10A is a schematic waveform of the relationship between switchswitching and a DC current in a switching cycle when one voltage commandis controlled to reach a peak value under the AZSVPWM switchingaccording to the present disclosure.

FIG. 10B is a schematic waveform of the relationship between switchswitching and a DC current in a switching cycle when one voltage commandis controlled to reach a valley value under the AZSVPWM switchingaccording to the present disclosure.

FIG. 11A is a space vector diagram composed of voltage vectors under theoperation of FIG. 10A.

FIG. 11B is a space vector diagram composed of voltage vectors under theoperation of FIG. 10B.

FIG. 12 is a block diagram of the system structure of the pulse widthmodulation applied to the power converter according to the presentdisclosure.

FIG. 13 is a flowchart of a method of controlling the power converteraccording to the present disclosure.

DETAILED DESCRIPTION

Reference will now be made to the drawing figures to describe thepresent disclosure in detail. It will be understood that the drawingfigures and exemplified embodiments of present disclosure are notlimited to the details thereof.

As mentioned above, the power converter is used to convert electricalenergy between the DC side and the AC side in various applications. Thepower converter is composed of a power switch module, which achieveselectrical energy conversion by switching a plurality of switches. Asshown in FIG. 1 , for example, the input power output from the battery200 shown in FIG. 1 is converted into the three-phase output power. Thetechnology proposed in the present disclosure is a switching technologyapplied to a traditional three-phase power converter. In otherembodiments, the input power may be direct current (DC), single-phasealternating current (AC), three-phase alternating current (AC), ormulti-phase alternating current (AC), etc., but the present disclosureis not limited thereto.

Please refer to FIG. 2 , which shows a conventional power converterincluding a DC-side capacitor C_(dc). A current i_(DC, inv) flowingthrough the DC-side capacitor C_(dc) (referred to as, DC-side capacitorcurrent i_(DC, inv) later) is affected by the switching of thethree-phase switches, and it is expressed in formula (1) as follows.

i _(DC,inv) =S _(u) ·i _(u) +S _(v) ·i _(v) +S _(w) ·i _(w)  (1)

In which, S_(u), S_(v), S_(w) represent switching status of each arm.Take the U phase of FIG. 2 as an example, when the upper arm switch(S_(u1)) is turned on, S_(u)=1; conversely, when the lower arm switch(S_(u2)) is turned on, S_(u)=0. The effective value (root-mean-squarevalue) of the DC-side capacitor current i_(DC, inv, rms) is calculatedas follows.

i _(DC,inv,rms)=1/T _(sw)∫(i _(DC,inv))² dt  (2)

It is assumed that the voltage command falls in the triangle intervalcomposed of v₁, v₂, v₀, v₇. According to the switching manner of thethree arms and the corresponding output current, the relationshipbetween the voltage vector and the DC-side capacitor current i_(DC, inv)may be sorted as shown in Table 2.

TABLE 2 voltage vectors DC-side capacitor current i_(DC, inv) v₁ i_(u)v₂ −i_(w ) v₃ i_(v) v₄ −i_(u)  v₅  i_(w) v₆ −i_(v)  v₀, v₇ 0

Table 3 defines the current interval according to the polarity of theoutput current of the power converter (it is assumed that thethree-phase current is balanced), and the maximum absolute value of thethree-phase current in each current interval is i_(max).

TABLE 3 current intervals (R_(cur)) i_(u) i_(v) i_(w) i_(max) I >0 <0 <0i_(u) II >0 >0 <0  i_(w) III <0 >0 <0 i_(v) IV <0 >0 >0 i_(u) V <0 <0 >0 i_(w) VI >0 <0 >0 i_(v)

Please refer to FIG. 13 , which shows a method of controlling the powerconverter according to the present disclosure, and also refer to FIG. 7and FIG. 8B. In step (S11) of FIG. 13 , the three-phase output commandv_(u)*, v_(v)*, v_(w)* corresponding to the three-phase output power isacquired.

Afterward, refer to FIG. 8A and FIG. 8B, in step (S12), according to thethree-phase output command v_(u)*, v_(v)*, v_(w)* and the controlcarrier ePWM, ePWM′, the voltage phase angle θ corresponding to thethree-phase output command v_(u)*, v_(v)*, v_(w)* is acquired. As shownin FIG. 8B, the control carrier includes a first triangle wave ePWM anda second triangle wave ePWM′, and a phase difference between the firsttriangle wave ePWM and the second triangle wave ePWM′ is π. Therefore,as shown in FIG. 9 , the AZSVPWM control is executed to acquire thevoltage phase angle θ corresponding to the three-phase output commandv_(u)*, v_(v)*, v_(w)* located on a two-phase axis coordinate (i.e., d-qaxis coordinate) according to the three-phase output command v_(u)*,v_(v)*, v_(w)*, the first triangular wave ePWM, and the secondtriangular wave ePWM′.

Please refer to FIG. 8A, which shows a schematic waveform of therelationship between switch switching and a DC current in a switchingcycle under traditional SVPWM switching. In comparison with the SVPWMswitching technique shown in FIG. 8A, the AZSVPWM switching techniqueshown in FIG. 8B uses two carriers, i.e., one is the same carrier ePWMas in FIG. 8A, and the other is the reverse carrier ePWM′. Therelationship between AZSVPWM switching and DC current is shown in FIG.8B. In general, traditional power converters use electrolytic capacitorsas DC-side capacitors C_(dc). The larger the effective value of theDC-side capacitor current i_(DC, inv, rms), the greater the heat thatthe DC-side capacitors C_(dc) need to withstand, and therefore thelarger the electrolytic capacitor is needed to avoid excessivetemperature. Accordingly, by reducing the DC-side capacitor currenti_(DC, inv) can reduce the size of the electrolytic capacitor, therebyreducing the cost of the product.

The technology proposed by the present disclosure is to reduce thecurrent ripple of the DC-side capacitors C_(dc) of the power converterby introducing the zero-sequence voltage in an appropriate interval whenthe power converter operates based on the AZSVPWM switching technology,thereby effectively increasing the stability and performance of thepower converter in operation. Take the operation condition (the voltageinterval R_(vol) is in I and the current interval R_(cur) is in I) asshown in FIG. 8B as an example: it can be analyzed that in a switchingcycle, the composition of the voltage is v₁, v₂, v₃, v₆ and the zerovector. If explained with the vector diagram of FIG. 6 , the outputvoltage command may be composed of the half-plane voltage vector underthe AZSVPWM operation, as shown in FIG. 9 .

Furthermore, a three-phase current value i_(u), i_(v), i_(w) of thethree-phase output power is acquired (S13). Afterward, in step (S14),the voltage phase angle θ and a positive/negative change of thethree-phase current value i_(u), i_(v), i_(w) is detected to decide thata zero-sequence voltage is a positive voltage, a zero voltage, or anegative voltage. Specifically, refer to FIG. 8B, FIG. 9 , and Table 4,the control method further includes: determining one of the pluralitiesof phase intervals into which the voltage phase angle θ falls as theworking voltage region.

The controller 400 builds a table (or called a look-up table), anddetermines the voltage phase angle and the positive/negative change ofthe three-phase current value to determine whether the zero-sequencevoltage is the positive voltage, the zero voltage, or the negativevoltage by querying the table. In particular, the table includes aplurality of voltage intervals and a plurality of current intervals, andeach voltage interval is corresponding to the plurality of currentintervals, as shown in Table 4. Each voltage interval of the tablecorrespondingly records a plurality of phase intervals. Each currentinterval of the table records the positive/negative change of thethree-phase current value. The table records the zero-sequence voltagecorresponding to each current interval in the different voltageintervals is the positive voltage, the zero voltage, or the negativevoltage.

The detailed determination steps are as follows: determining that thevoltage phase angle falls into one of the plurality of phase intervals;afterward, selecting correspondingly the voltage interval correspondingto one of the plurality of phase intervals in the table; afterward,receiving and determining the positive/negative change of thethree-phase current value, and selecting the corresponding currentinterval in the table; finally, querying the table to decide that thezero-sequence voltage is the positive voltage, the zero voltage, or thenegative voltage according to the selected voltage interval and theselected current interval.

In particular, the plurality of phase intervals include a first phaseinterval [0, π/3] (i.e., [0, 60°]), a second phase interval [π/3, 2π/3](i.e., [60°, 120°]), a third phase interval [2π/3, π] (i.e., [120°, 180°]), a fourth phase interval [π, 4π/3] (i.e., [180°, 240° ]), a fifthphase interval [4π/3, 5π/3] (i.e., [240°, 300° ]), and a sixth phaseinterval [5π/3, 2π] (i.e., [300°, 360° ]).

Specifically, refer to Table 3 and Table 5. When a U-phase current ofthe three-phase current value is positive, a V-phase current isnegative, and a W-phase current is negative, the three-phase currentvalue is recorded as a first current interval of the plurality ofcurrent intervals. When the U-phase current of the three-phase currentvalue is positive, the V-phase current is positive, and the W-phasecurrent is negative, the three-phase current value is recorded as asecond current interval of the plurality of current intervals. When theU-phase current of the three-phase current value is negative, theV-phase current is positive, and the W-phase current is negative, thethree-phase current value is recorded as a third current interval of theplurality of current intervals. When the U-phase current of thethree-phase current value is negative, the V-phase current is positive,and the W-phase current is positive, the three-phase current value isrecorded as a fourth current interval of the plurality of currentintervals. When the U-phase current of the three-phase current value isnegative, the V-phase current is negative, and the W-phase current ispositive, the three-phase current value is recorded as a fifth currentinterval of the plurality of current intervals. When the U-phase currentof the three-phase current value is positive, the V-phase current isnegative, and the W-phase current is positive, the three-phase currentvalue is recorded as a sixth current interval of the plurality ofcurrent intervals.

TABLE 4 voltage intervals current intervals zero-sequence voltage(R_(vol)) (R_(cur)) (v_(z)*) I I, IV v_(z1)*(+) II, V v_(z2)*(−) III, VI0 II II, V v_(z2)*(−) III, VI v_(z1)*(+) I, IV 0 III III, VI v_(z1)*(+)I, IV v_(z2)*(−) II, V 0 IV I, IV v_(z2)*(−) II, V v_(z1)*(+) III, VI 0V II, V v_(z1)*(+) III, VI v_(z2)*(−) I, IV 0 VI III, VI v_(z2)*(−) I,IV v_(z1)*(+) II, V 0

In Table 4, (+) represents the positive voltage, (−) represents thenegative voltage, and 0 represents the zero voltage.

Preferably, in step (S14) of FIG. 13 , when the zero-sequence voltage isdecided to be the positive voltage, the control method further includessteps of: acquiring a peak value of the control carrier ePWM, ePWM′ in aswitching cycle; afterward, acquiring a maximum voltage command of thethree-phase output command v_(u)*, v_(v)*, v_(w)*; afterward,calculating a first voltage difference between the peak value and themaximum voltage command as a magnitude of the positive voltage of thezero-sequence voltage. As shown in FIG. 10A, which shows a schematicwaveform of the relationship between switch switching and a DC currentin a switching cycle when one voltage command is controlled to reach apeak value under the AZSVPWM switching according to the presentdisclosure. For example, after the voltage command is introduced into azero-sequence voltage (v_(z)*=v_(z1)*=Tri-max (v_(u)*, v_(v)*, v_(w)*)),the original maximum voltage command (i.e., v_(u)*) is pushed to the topof the control carrier ePWM so that the switch of this phase fully isturned on during this switching cycle. In this condition, the outputvoltage command is only composed of v₂, v₆, and the zero vector, asshown in FIG. 11A.

Preferably, in step (S14) of FIG. 13 , when the zero-sequence voltage isdecided to be the negative voltage, the control method further includessteps of: acquiring a valley value of the control carrier ePWM, ePWM′ ina switching cycle; afterward, acquiring a minimum voltage command of thethree-phase output command v_(u)*, v_(v)*, v_(w)*; afterward,calculating a second voltage difference between the valley value and theminimum voltage command as a magnitude of the negative voltage of thezero-sequence voltage. As shown in FIG. 10B, which shows a schematicwaveform of the relationship between switch switching and a DC currentin a switching cycle when one voltage command is controlled to reach avalley value under the AZSVPWM switching according to the presentdisclosure. For example, after the voltage command is introduced into azero-sequence voltage (v_(z)*=v_(z2)*=−min (v_(u)*, v_(v)*, v_(w)*)),the original minimum voltage command (i.e., v_(w)*) is pulled to thebottom of the control carrier ePWM so that the switch of this phasefully is turned off during this switching cycle. In this condition, theoutput voltage command is only composed of v₁, v₃, and the zero vector,as shown in FIG. 11B.

Therefore, if the DC-side capacitor current i_(DC, inv) wants to bereduced, it is necessary to reduce the voltage vector interval thatgenerates the maximum DC current. Take the operation condition (thevoltage interval R_(vol) is in I and the current interval R_(cur) is inI) as shown in FIG. 8B as an example: the maximum capacitor current isi_(u) and the voltage vector is v₁ at this time. If the magnitude of theDC current wants to be reduced without affecting the output voltage, anappropriate zero-sequence voltage (v_(z1)*) is introduced to eliminatev₁ to reduce the DC current by the AZSVPWM, as shown in FIG. 10A.

If the zero-sequence voltage v_(z2)* in FIG. 10A is introduced at thistime, the original maximum DC current vector will become larger andcannot reduce the effective value (root-mean-square value) of theDC-side capacitor current i_(DC, inv, rms). Similarly, if the operationcondition at this time is that the current interval R_(cur) is in II, anappropriate zero-sequence voltage (v_(z2)*) is introduced to eliminatev₂ to reduce the DC current by the AZSVPWM, as shown in FIG. 10A.However, if the operation condition is that the current interval R_(cur)is in III, that maximum current is iv as shown in Table 3. Under thisoperation condition, regardless of introducing v_(z1)* or v_(z2)*according to Table 1, the voltage command will be synthesized by voltagevectors with the (maximum) DC current of i_(v), and therefore there isno any zero-sequence voltage needs to be introduced at this time, i.e.,v_(z)*=0.

According to the above-mentioned analysis, if this method is extended toconsider the all combinations of voltage intervals and currentintervals, Table 4 sorts the combinations according to different voltageintervals and current intervals (Table 1 to Table 3) to realize thatwhat kind of zero-sequence voltage may be introduced to effectivelyreduce the effective value (root-mean-square value) of the DC-sidecapacitor current i_(DC, inv, rms). Therefore, this is the pulse widthmodulation that introduces local interval zero-sequence voltage proposedby the present disclosure, and the implemented system structure diagramis shown in FIG. 12 . The controller 400 feeds back the current of thepower converter, and determines the intervals between the current andthe voltage command generated by itself. Also, according to Table 4, thezero-sequence voltage calculation unit 600 calculates the appropriatezero-sequence voltage to add to the voltage command, and finallyachieves the low DC-side capacitor current through the implementation ofAZSVPWM. The technology of the present disclosure is based on AZSVPWMthat generates PWM signals through simple command and control carriercomparison, and does not require complicated calculations as describedin the prior art to achieve the purpose of reducing the capacitorcurrent.

In step (S15) of FIG. 13 , the zero-sequence voltage and the three-phaseoutput command v_(u)*, v_(v)*, v_(w)* are composed to acquire thethree-phase output expected value. Afterward, the three-phase expectedvalue with the control carrier are compared to acquire a turned-on timeof each switch (S16) so as to adjust the three-phase output power byswitching (converting) the input power according to the turned-on timeof each switch (the upper arm switches S_(u1), S_(v1), S_(w1) and thelower arm switches S_(u2), S_(v2), S_(w2)). In other words, the powerconverter 100 includes the DC-side capacitor C_(dc) coupled to theswitches (S_(u1), S_(v1), S_(w1) and S_(u2), S_(v2), S_(w2)), and thecontroller 400 compares the three-phase expected value with the controlcarrier to acquire the turned-on time corresponding to each switch(S_(u1), S_(v1), S_(w1) and S_(u2), S_(v2), S_(w2)) to reduce thecurrent ripple of the DC-side capacitor C_(dc). Accordingly, the controlmethod of the power converter proposed by the present disclosure isbased on the AZSVPWM technology, and the zero-sequence voltage isintroduced in an appropriate interval to reduce the current ripple ofthe DC-side capacitor C_(dc), thereby effectively increasing thestability and performance of the operation of the power converter.

Although the present disclosure has been described with reference to thepreferred embodiment thereof, it will be understood that the presentdisclosure is not limited to the details thereof. Various substitutionsand modifications have been suggested in the foregoing description, andothers will occur to those of ordinary skill in the art. Therefore, allsuch substitutions and modifications are intended to be embraced withinthe scope of the present disclosure as defined in the appended claims.

What is claimed is:
 1. A method of controlling a power converter, thepower converter configured to convert an input power to generate athree-phase output power through a plurality of switches, the methodcomprising steps of: acquiring a three-phase output commandcorresponding to the three-phase output power, comparing the three-phaseoutput command with a control carrier to acquire a voltage phase anglecorresponding to the three-phase output command according to thecomparison result, acquiring a three-phase current value of thethree-phase output power, detecting the voltage phase angle and apositive/negative change of the three-phase current value to decide thata zero-sequence voltage is a positive voltage, a zero voltage, or anegative voltage, composing the zero-sequence voltage and thethree-phase output command to acquire a three-phase output expectedvalue, comparing the three-phase expected value with the control carrierto acquire a turned-on time of each switch, and switching the inputpower to adjust the three-phase output power according to the turned-ontime of each switch.
 2. The method as claimed in claim 1, furthercomprising steps of: building a table by a controller, and determiningthe voltage phase angle and the positive/negative change of thethree-phase current value to query the table to decide that thezero-sequence voltage is the positive voltage, the zero voltage, or thenegative voltage, wherein the table comprises a plurality of voltageintervals and a plurality of current intervals, and each voltageinterval is corresponding to the plurality of current intervals, whereineach voltage interval of the table correspondingly records a pluralityof phase intervals, each current interval of the table records thepositive/negative change of the three-phase current value, and the tablerecords the zero-sequence voltage corresponding to each current intervalin the different voltage intervals is the positive voltage, the zerovoltage, or the negative voltage.
 3. The method as claimed in claim 2,further comprising steps of: determining that the voltage phase anglefalls into one of the pluralities of phase intervals, selectingcorrespondingly the voltage interval corresponding to one of thepluralities of phase intervals in the table, receiving and determiningthe positive/negative change of the three-phase current value, andselecting the corresponding current interval in the table, and queryingthe table to decide that the zero-sequence voltage is the positivevoltage, the zero voltage, or the negative voltage according to theselected voltage interval and the selected current interval.
 4. Themethod as claimed in claim 2, wherein the plurality of phase intervalscomprises a first phase interval [0, π/3], a second phase interval [π/3,2π/3], a third phase interval [2π/3, π], a fourth phase interval [π,4π/3], a fifth phase interval [4π/3, 5π/3], and a sixth phase interval[5π/3, 2π].
 5. The method as claimed in claim 2, further comprisingsteps of: recording the three-phase current value as a first currentinterval of the plurality of current intervals when a U-phase current ofthe three-phase current value is positive, a V-phase current isnegative, and a W-phase current is negative, recording the three-phasecurrent value as a second current interval of the plurality of currentintervals when the U-phase current of the three-phase current value ispositive, the V-phase current is positive, and the W-phase current isnegative, recording the three-phase current value as a third currentinterval of the plurality of current intervals when the U-phase currentof the three-phase current value is negative, the V-phase current ispositive, and the W-phase current is negative, recording the three-phasecurrent value as a fourth current interval of the plurality of currentintervals when the U-phase current of the three-phase current value isnegative, the V-phase current is positive, and the W-phase current ispositive, recording the three-phase current value as a fifth currentinterval of the plurality of current intervals when the U-phase currentof the three-phase current value is negative, the V-phase current isnegative, and the W-phase current is positive, and recording thethree-phase current value as a sixth current interval of the pluralityof current intervals when the U-phase current of the three-phase currentvalue is positive, the V-phase current is negative, and the W-phasecurrent is positive.
 6. The method as claimed in claim 1, wherein whenthe zero-sequence voltage is decided to be the positive voltage, themethod further comprises steps of: acquiring a peak value of the controlcarrier in a switching cycle, acquiring a maximum voltage command of thethree-phase output command, and calculating a first voltage differencebetween the peak value and the maximum voltage command as a magnitude ofthe positive voltage of the zero-sequence voltage.
 7. The method asclaimed in claim 1, wherein when the zero-sequence voltage is decided tobe the negative voltage, the method further comprises steps of:acquiring a valley value of the control carrier in a switching cycle,acquiring a minimum voltage command of the three-phase output command,and calculating a second voltage difference between the valley value andthe minimum voltage command as a magnitude of the negative voltage ofthe zero-sequence voltage.
 8. The method as claimed in claim 1, whereinthe control carrier comprises a first triangle wave and a secondtriangle wave, and a phase difference between the first triangle waveand the second triangle wave is π.
 9. The method as claimed in claim 8,further comprising a step of: executing an AZSVPWM control to acquirethe voltage phase angle corresponding to the three-phase output commandlocated on a two-phase axis coordinate according to the three-phaseoutput command, the first triangle wave, and the second triangle wave.10. The method as claimed in claim 1, wherein the power convertercomprises a DC-side capacitor, and the DC-side capacitor is coupled toeach of the switches, and the method further comprises a step of:acquiring the turned-on time of each switch by comparing the three-phaseoutput expected value with the control carrier to reduce a currentripple of the DC-side capacitor.
 11. A power converter comprising: aplurality of switches configured to convert an input power to generate athree-phase output power, and a controller comprising a control carrier,wherein the controller is configured to acquire a three-phase outputcommand corresponding to the three-phase output power, and acquire avoltage phase angle corresponding to the three-phase output command,wherein the controller is configured to detect a positive/negativechange of a three-phase current value of the three-phase output power,wherein the controller is configured to build a table, and the tablecomprises a plurality of voltage intervals and a plurality of currentintervals, and each voltage interval is corresponding to the pluralityof current intervals, wherein each voltage interval of the tablecorrespondingly records a plurality of phase intervals, each currentinterval of the table records the positive/negative change of thethree-phase current value, and the table records the zero-sequencevoltage corresponding to each current interval in the different voltageintervals is a positive voltage, a zero voltage, or a negative voltage,wherein the controller queries the table to determine the voltageinterval in which the voltage phase angle falls according to the voltagephase angle and the three-phase current value, and decides that thezero-sequence voltage is the positive voltage, the zero voltage, or thenegative voltage according to the current interval corresponding to thepositive/negative change of the three-phase current value, wherein thecontroller composes the zero-sequence voltage and the three-phase outputcommand to acquire a three-phase output expected value, and compares thethree-phase expected value with the control carrier to acquire aturned-on time of each switch.
 12. The power converter as claimed inclaim 11, wherein the plurality of phase intervals comprises a firstphase interval [0, π/3], a second phase interval [π/3, 2π/3], a thirdphase interval [2π/3, π], a fourth phase interval [π, 4π/3], a fifthphase interval [4π/3, 5π/3], and a sixth phase interval [5π/3, 2π]. 13.The power converter as claimed in claim 11, wherein when a U-phasecurrent of the three-phase current value is positive, a V-phase currentis negative, and a W-phase current is negative, the controller recordsthe three-phase current value as a first current interval of theplurality of current intervals, when the U-phase current of thethree-phase current value is positive, the V-phase current is positive,and the W-phase current is negative, the controller records thethree-phase current value as a second current interval of the pluralityof current intervals, when the U-phase current of the three-phasecurrent value is negative, the V-phase current is positive, and theW-phase current is negative, the controller records the three-phasecurrent value as a third current interval of the plurality of currentintervals, when the U-phase current of the three-phase current value isnegative, the V-phase current is positive, and the W-phase current ispositive, the controller records the three-phase current value as afourth current interval of the plurality of current intervals, when theU-phase current of the three-phase current value is negative, theV-phase current is negative, and the W-phase current is positive, thecontroller records the three-phase current value as a fifth currentinterval of the plurality of current intervals, and when the U-phasecurrent of the three-phase current value is positive, the V-phasecurrent is negative, and the W-phase current is positive, the controllerrecords the three-phase current value as a sixth current interval of theplurality of current intervals.
 14. The power converter as claimed inclaim 11, wherein when the controller decides that the zero-sequencevoltage is the positive voltage, the controller further: acquires a peakvalue of the control carrier in a switching cycle, acquires a maximumvoltage command of the three-phase output command, and calculates afirst voltage difference between the peak value and the maximum voltagecommand as a magnitude of the positive voltage of the zero-sequencevoltage.
 15. The power converter as claimed in claim 11, wherein whenthe controller decides that the zero-sequence voltage is the negativevoltage, the controller further: acquires a valley value of the controlcarrier in a switching cycle, acquires a minimum voltage command of thethree-phase output command, and calculates a second voltage differencebetween the valley value and the minimum voltage command as a magnitudeof the negative voltage of the zero-sequence voltage.
 16. The powerconverter as claimed in claim 11, wherein the control carrier comprisesa first triangle wave and a second triangle wave, and a phase differencebetween the first triangle wave and the second triangle wave is π,wherein the controller executes an AZSVPWM control to acquire thevoltage phase angle corresponding to the three-phase output commandlocated on a two-phase coordinate axis according to the three-phaseoutput command, the first triangle wave, and the second triangle wave.17. The power converter as claimed in claim 11, further comprising: aDC-side capacitor coupled to each of the switches, wherein thecontroller compares the three-phase output expected value with thecontrol carrier to acquire the turned-on time corresponding to eachswitch to reduce a current ripple of the DC-side capacitor.